the theory that all matter will again collapse to form the dense material.
The singularity at the end of the universe.
Essentially the opposite of the Big Bang, the Big Crunch is one possible fate of the Universe. If the matter and energy of the Universe are not moving outward quickly enough, gravity could pull the Universe in on itself, collapsing it in a final Big Crunch. It is not yet known whether this will happen to our Universe.
This is one possible fate for the universe among many, where the whole universe collapses to a singularity.
The big crunch is the collapse of all of the matter in the universe - a reversal of the big bang. This is one hypothesized future of the universe, assuming that the universe is closed (having a mass density exceeding the critical mass density).
Collapse of the Universe into its original form before the Big Bang. At the end of this process matter, energy, space, and time will not exist.
A potential fate of the universe in which the observed expansion of the universe is halted by gravity; gravity then pulls the universe back into a singularity.
In physical cosmology, the Big Crunch is the hypothesis that the universe will collapse upon itself after its expansion eventually stops — a counterpart to the Big Bang. This hypothesis is the subject of much heated discussion.